1. Field of the Invention
The invention relates generally to the field of aqueous dispersions of globules which comprise aqueous components. It relates, in part, to the field of multi-phase coating compositions which can be used to produce textured or multicolored coatings, ceramic glazes and fibrous webs, and on volatilization to produce dry granules.
2. Description of the Prior Art
Dispersions of macro size aqueous globules have been made previously by incorporating a hydrophilic colloid in a first aqueous phase, and incorporating in a second aqueous phase one or more insolubilizing agents for said colloid which render it insoluble in the second aqueous phase. Means for doing this are disclosed in U.S. Pat. Nos. 3,458,328, 3,725,089, and 3,852,076.
In prior art the reactions responsible for insolubilization have been either exclusively or predominantly either noncolloidal or nonionic in character, or both.
By "noncolloidal" reactions I mean those in which at least one of the reactants is noncolloidal in nature. For example, the reaction between galactomannoglycans such as guar gum or locust bean gum and water soluble borates is noncolloidal because water soluble salts are not colloidal.
By "nonionic" reactions I mean those in which reactive groups of at least one of the reactants are nonionic, or in which reactive groups of both reactants bear the same kind of charge. For example, the reaction between colloidal clay and hydroxyethyl cellulose is nonionic, even though the colloidal clay is anionic.
The term "ionic reaction" as used herein refers to one in which both reactants are ionic and opposite in charge. For example, reactions beteen cationic and anionic colloids are ionic.
There are inherent strength limitations in membranes or matrices formed by means of nonionic reactions, since they are dependent on intermolecular forces which are relatively weak compared to ionic forces. Where the dispersions are subject to high shear forces as in brushing or high pressure spraying, it is desirable to provide globules which can withstand such forces without breaking, yet have relatively fluid or pliable characteristics.
There are limitations also with respect to insolubilization by means of noncolloidal reactions. The effect of salts or other noncolloidal compounds on organic colloids is generally to form poorly hydrated flocculates rather than flowable globules. In the few cases where hydrous gels are formed, there is a tendency for the reaction to propagate throughout the interior of the insolubilized globules, and the degree of gelation is difficult to control.
Globules of superior strength and desired fluidity are produced in the present invention by means of reactants which are both colloidal and ionic. It is believed that improved properties result from the ability of such materials to react strongly and primarily at the interface when this is required, or by the desired degree of reaction throughout the globule.
Globule characteristics are particularly significant in dispersions intended for coating applications. Several kinds of dispersions have been found acceptable for spray application, but deficient in application by brush or roller. Inadequacy in this respect has generally been due to one or more of the following:
(a) inadequate resistance of globules to breakdown on shear,
(b) hard, gelatinous, or brittle consistencies of globules which give low surface drag and tendency to skid on smooth surfaces,
(c) inadequate separation of globules which aggravates skidding tendencies. This often results from interchange between dispersed and continuous phases, making it difficult to retain required viscosity and flow characteristics in the continuous phase.
By use of reactants which are both colloidal and ionic, the present invention makes possible a better separation of aqueous phases, with better control over both phases in order to provide the desired viscosity, globule size, strength and consistency, and coating application properties.
When somewhat similar materials have appeared in the prior art, it is clear that their significance has not been recognized. For example, the use of two ionic colloids of the same charge does not suggest the present invention. The use of ionic colloids of low molecular weight as thickeners does not suggest the present use, since optimum results are dependent on the use of ionic colloids of high molecular weight and superior reactivity. Some of these have only recently become commercially available. Likewise the present invention is not suggested by the presence of ionic reactants whose activity as insolubilizers is incidental and inadequate, with insolubilization primarily dependent on nonionic or noncolloidal reactions.